Metal working – Barrier layer or semiconductor device making
Reexamination Certificate
1995-08-20
2002-07-30
Graybill, David E (Department: 2827)
Metal working
Barrier layer or semiconductor device making
C118S500000, C118S728000
Reexamination Certificate
active
06425168
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a quartz glass jig, such as a quartz glass reaction tube (hereinafter referred to as a reaction tube) and a quartz glass wafer boat (hereinafter referred to as a wafer boat) that are used in a heat-treatment apparatus for semiconductor wafers, such as a CVD apparatus or a thermal diffusion apparatus.
More particularly, the present invention relates to a quartz glass jig, such as a reaction tube or a wafer boat, used in a thermal CVD apparatus.
2. Related Prior Art
Conventionally a CVD apparatus was well known in which a chemical reaction in a activated space was used to form a thin film on a wafer or wafers.
There are, for example, a thermal CVD apparatus, a plasma CVD apparatus and a photo-assisted CVD apparatus which respectively use heat, plasma and ultraviolet light or laser as activation energies.
In a thermal CVD apparatus, vapor phase chemical reaction (for example, thermal decomposition, hydrogen reduction, oxidation or substitution reaction) at a high temperature of a volatile metal hologenide, a volatile metal organic compound or the like is conducted to form an epitaxial film made of semiconductor such as silicon or a metal having a high melting point, or an insulating film or a protection film made of the oxide of semiconductor such as silicon on a wafer or wafers.
Jigs such as a reaction tube and a wafer boat used in such CVD apparatuses are generally made of quartz glass from the requirements for chemical stability and heat resistance.
In the vapor phase growth, since the surface or surfaces of a quartz glass jig are exposed to a vapor phase growth space in the apparatus, a thin film or films adhere on the surface or surfaces of the jig as well as the surface of a wafer or wafers.
A reaction temperature of the vapor phase chemical reaction required for thermal decomposition of SiH
4
, which is used for formation of a Si thin film in a thermal CVD method, is in the range of 500° C. to 1100° C.
A reaction temperature of the vapor phase chemical reaction for reduction of SiCl
4
is upto 1200° C.
What's more, because the thermal expansion coefficients of a Si film and quartz glass, which is the material of a reaction tube, are different from each other by one figure or so, the film has a risk to get separate due to a stress caused by the difference between the expansion coefficients, when a CVD film is thin.
On the other hand, when the CVD film is thick and the stress affecting the quartz glass of the reaction tube is larger, the reaction tube, this time, has a risk to break.
This is also the case with not only a CVD apparatus but also a diffusion furnace in which the heat-treatment space is under influence of a high temperature of about 1200° C., and especially the above-mentioned adverse effects is conspicuously observed in a CVD apparatus in which thin films adhere on surfaces.
In the case of a wafer boat in the reaction tube aforementioned where wafers are disposed in a stacking manner at respective predetermined positions, boat marks (which means poor exterior appearance observed on the surface or surfaces of a wafer caused by contacting with the boat and sometimes are accompanied by chipping along the periphery of a wafer) often occur at a contacting portion or portions between the periphery of each of the wafers and the boat, because the peripheries of the wafers and the boat are in the contacting conditions of planes or lines and move over each other with friction due to the difference between the thermal expansion coefficients.
SUMMARY OF THE INVENTION
The present invention was made to solve the technical faults of the prior art.
It is an object of the present invention to provide a quartz glass jig used for a heat-treatment apparatus for semiconductor wafers, in particular a CVD apparatus, and a method for producing the jig that can solve various faults caused by the difference between the thermal expansion coefficients of the aforementioned thin film and the quartz glass jig.
It is another object of the present invention to provide a reaction tube to be used in a CVD apparatus in which neither crack nor breakdown occurs, even when a thin film adheres on the internal wall or walls of the reaction tube.
It is a further object of the present invention to provide a wafer boat to be used in a CVD apparatus in which neither boat mark on nor chippings along the periphery of a wafer or wafers occur.
The present invention is applied to a quartz glass jig to be used in a heat-treatment apparatus, in particular a CVD apparatus, and is characterized in that the jig is made of transparent quartz glass as the material and that sand-blasting is given on the portion or portions exposed to the heat-treatment space.
The reason why the material of the jig is limited to transparent quartz glass is that transparent quartz glass has a more uniform surface hardness in comparison with bubble-mixed or opaque quartz glass and a desired surface roughness is effectively achieved in sand-blasting, so that the faults resulted from the stress occurred between the CVD film and a treated surface or surfaces of the jig are effectively prevented.
In the present invention, in a more concrete manner, in the case of a reaction tube
1
used in a thermal CVD apparatus in
FIG. 1
, at least the portion or portions which are heated by a heater
2
of the internal wall
10
a
are preferably sand-blasted and in the case of a wafer boat
20
used in a thermal CVD apparatus in
FIG. 2
, at least the portions of the wafer boat
20
that contact with each wafer
30
are preferably sand-blasted.
According to the present invention, the center-line mean roughness (Ra) of the surface after sand-blasting is set in the range of 1 &mgr;m to 20 &mgr;m, preferably 2 &mgr;m to 10 &mgr;m, more preferably 3 &mgr;m to 5 &mgr;m. It is still more preferable that the maximum height (Rmax) is roughly set in the range of 10 &mgr;m to 30 &mgr;m, while the center-line mean roughness (Ra) is set in the range of 3 &mgr;m to 5 &mgr;m.
Abrasive material used in sand-blasting is made of a material or a mixture of materials that are harder than quartz glass and do not become a contamination source or sources, for example, crystallized quartz powders or SiC powders and the grit size distribution is preferably set so that the weight in the range of 100 &mgr;m to 400 &mgr;m in grit size is at 90% of the total weight.
Such a function of the present invention will be explained in reference to FIG.
3
(
a
) and FIG.
3
(
b
) below:
For example, a case that a poly silicon film
40
adheres on the internal wall surface
10
a
of a reaction tube
10
in a CVD method is here considered referring to FIG.
3
(
a
).
Since the linear expansion coefficient of Si is 4.7×10
−6
/° C. to 4.9×10
−6
/° C. and that of SiO2 is 5.5×10
−7
/° C., thermal contraction of the poly silicon thin film
40
occurs, but that of quartz almost no way occur, when the temperature is lowered from any in the range of 550° C. to 770° C. to room temperature of 20° C. during CVD growth.
In this circumstance, the poly silicon thin film
40
makes a compressive stress A occur in the quartz glass
10
and on the other hand the quartz glass
10
makes a tensile stress B occur in the poly silicon thin film
40
.
The thermal stress A, which the poly silicon thin film
40
gives to the quartz glass
10
, accordingly is obtained from the following equation:
A=E
(&agr;1−&agr;2)&Dgr;
T
=(1.9~2.4)×10
8
dyne/cm
2
,
where E: Young's modulus of poly silicon thin film
40
(0.9×10
11
dyne/cm
2
)
&agr;1: linear expansion coefficient of poly silicon thin film
40
(4.5−10
−6
/° C.)
&agr;2: linear expansion coefficient of quartz (5.5×10
−7
/° C.)
&Dgr;T: (550~700)−20=530~680° C.
If the thermal stress A is (1.9~2.4)×10
8
dyne/cm
2
, this value exceeds the design stress for a reaction tube and the breakdown thereof thus becomes a real risk, in the case that the dimensions of the reac
Baker & Daniels
Graybill David E
Shin-Etsu Handotai & Co., Ltd.
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